That might depend on your set up and how much room you have for them in addition to type of breeds you keep.

I have 3 chickens and 4 bantams. The chickens are obviously the rulers of the coop and the bantams submit or just stay to themselves. They don't "hang out" together but there is no bullying. Everyone is happy and healthy but the tend to segregate themselves from each other. They do roost together with no issues and all share the same nest for laying eggs by taking turns. I have enough nests available, it just seems only one is everyone's favorite.

ETA: I would not have a full size rooster in with the bantams. A large rooster could potentially kill a bantam if it tries to mate with one.

X2 on Free Spirit's advice. Sometimes it will work (if they have plenty of space), but it's always risky as the bantams are liable to take a beating from the larger standard breeds. For this reason, we had to move our bantam Cochins and Silkies out of the main flock and keep them in their own separate enclosure.